The anisotropic etch rate of p-type single crystal silicon has been systematically studied as a function of an externally applied electrical potential. Changes in overall etch rate are consistent with a combined chemical etching and electrochemical oxidation mechanism. Etch rate results of orientations close to (111) indicate that, at these surfaces, etching follows a step mechanism. Additionally it shows a difference in reactivity between monohydride and dihydride terminated steps towards both chemical etching and electrochemical oxidation. Morphology changes have also been observed, in particular on (110) surface, where the macroscopic surface becomes smoother at positive bias.